EXOD427 One who speaks lashon hara about his oldest brother, his mother's husband, or his father's wife also transgresses the commandment to honor one’s parents, for Chazal (Kesubos 103a) derive--from the word וְאֶת in the pasuk: כַּבֵּ֥ד אֶת־אָבִ֖יךָ וְאֶת־אִמֶּ֑ךָ, “Honor your father and your mother” (Shemos 20:12)--that there is an obligation to honor these individuals. If one speaks lashon hara about his actual father or mother, Heaven forbid, then he certainly transgresses the commandment to honor one's parents, and as also is subject to the curse of ארור מקלה אביו ואמו, “Cursed is one who disgraces his father or mother” (Devarim 27:26), Hashem should protect us.